The speculation for a few decades has been … that we have farmed the heck out of the same land so long… never giving it time to go fallow for long periods; use chemical fertilizers… which tend to kill the natural microorganisms that help ‘make good soil’; and even the artificial stuff tends to NOT put the significant (and necessary to the body) trace elements that were once part of the ‘standard’ veggie spread.
Only those places where organic methods have been used and the soil nurtured ‘back to health’ have shown improvements in the important percentages.
Sadly, the industry tends to go for fast, shippable, less spoilage — which usually means — chemicals, forced growth ‘hot house’ produce. I keep telling my kids that a home grown ‘real’ tomato actually has TASTE compared to the watery, semi square (easier to pack) blobs one finds at most stores. One day they’ll actually listen to their dinosaur era dad!